This invention relates to apparatus for feeding flock fibers. More specifically, this invention relates to apparatus for feeding flock fibers at a variably controlled rate for entrainment with a propelling air stream.
In the electrostatic flocking industry, flock fibers comprising relatively short, thin lengths of material such as nylon or rayon are delivered from a bulk supply of fibers into the presence of an electrostatic field for deposition onto the surface of an adhesive-coated article. Desirably, the fibers are separated and aligned prior to deposition on the article, and are delivered to the article at a sufficient uniform rate to permit rapid coating with a flock surface of high quality. However, it is well known that flock fibers, unlike particles such as powdered paint, tend to clump together and become tangled when delivered from a bulk supply. This undesirably tends to clog the delivery equipment, and to cause incomplete fiber separation and alignment within the electrostatic field to yield flock surfaces of poor quality.
In the prior art, one common way to feed flock fibers from a bulk supply has been to use a so-called fluidic bed. A fluidic bed comprises a flock supply bin having air streams directed upwardly through the fibers to create a suspended fiber cloud. Alternately, timed air streams are directed downwardly onto the surface of a supply of fibers to create the fiber cloud. See, for example, U.S. Pat. No. 3,850,659. An electrostatic field is created in the vicinity of the fiber cloud whereby the fibers are deposited on the surface of the desired article, or alternately, an air stream is passed through the cloud to entrain a portion of the suspended fibers for direction toward the surface of the article. These fluidic beds are advantageous in that they are relatively inexpensive in construction, operation, and maintenance. However, the maximum rate at which fibers can be delivered to the surface of an article to be coated is undesirably slow. Moreover, it has been found that the flock flow rate with fluidic beds is relatively non-uniform to result in correspondingly non-uniform surface coatings.
Some flock feeding systems in the prior art have utilized various hopper constructions in an effort to improve the rate and uniformity of flock delivery. Some of these devices comprise a flock supply hopper having a relatively narrow discharge passage through which fibers are gravitationally fed. See, for example, U.S. Pat. Nos. 2,173,032 and 2,992,126. Such hoppers have not, however, provided the necessary separation of fibers to prevent clogging of the discharge passage, or to prevent small fiber clumps from being deposited on the surface of an article. Other hopper constructions have included a screen through which the fibers are fed. See, for example, U.S. Pat. Nos. 2,223,476; 2,358,227; 2,715,074; 3,411,931; 2,768,903; 3,551,178; and 3,889,636. The use of screens improves the separation of flock fibers and thereby helps prevent fiber tangling, but such screens also tend to block and undesirably restrict the feeding of flock fibers from the hopper to limit the maximum fiber flow rate.
Flock feeding apparatus has been proposed which utilizes augers or the like for screw-feeding flock fibers from a supply hopper into a chamber for entrainment with an air stream generated by a relatively large, high speed blower. See, for example, U.S. Pat. Nos. 2,718,207 and 2,889,805. With auger systems, the delivery of fibers from the supply hopper is relatively fast. However, such augers do not satisfactorily eliminate small clumps or tangles of fibers which tend to enter the air stream and become deposited upon the surface of the article being coated.
Still another prior art flock feeding system comprises a hopper with a discharge passage through which flock fibers are fed directly to a high speed blower. See, for example, U.S. Pat. No. 3,347,469. The fibers are entrained by the blower in a relatively high volume, high velocity stream of air for propulsion toward the surface of an article being coated. However, with such high speed blowers, it is necessary in electrostatic flocking to separate the high speed air stream from the fibers prior to deposition on the article. This prevents the high volume, high velocity air stream from detrimentally affecting the quality of surface finish. Such separation of the fibers from the air stream is not desirable, however, since the required screens and baffles tend to restrict the maximum flock flow rate. See for example, U.S. Pat. No. 3,551,178. Moreover, high speed blowers are relatively expensive to obtain and maintain.
This invention overcomes the problems and disadvantages of the prior art by providing a flock feeding apparatus which provides uniform, rapid flock delivery from a supply hopper without screens or other devices restricting fiber flow rate. This invention provides such uniform, rapid flock delivery without expensive high speed air blowers and without fiber clumping or tangling.